In flowing wells, the production is delivered from the formation to the surface through a tubing string. Tubing strings are normally fluid isolated from the well itself. This is to avoid communication of one geological formation to another. The integrity of the tubing string is quite important. After a period of time, small leaks may develop in the tubing string. One or more leaks will hamper production of the well and may create severe problems. The present invention is a pressure test apparatus which enables selected portions of the tubing string to be closed off and a pressure test run on the tubing thereabove.
Pressure testing of tubing strings is a preventive maintenance step which protects against catastrophic growth of leaks in a tubing string. For example, several tubing strings may be placed in a single well to communicate with different pay zones. The present invention enables testing of a tubing string at different horizons. Suppose, for example, that a tubing string is 10,000 feet long and communicates with a bottom hole zone of high pressure. It passes through two low pressure zones. Assume the well includes separate tubing strings to the low pressure zones which are isolated by suitable packer elements. Pressure from the 10,000 foot string leaked into the well may substantially cut production. However, a leak in the near vicinity of the low pressure zones will not only cut production from the high pressure zone, but the pressure may in fact overcome the low pressure zone fluid drive and reduce production from that zone almost to zero. The present invention is able to be run in a tubing string to pressure test the string. It is lowered in a string to a specified elevation. At the lowermost elevation, the device is landed at a collar and the pressure is tested. Leaks in the tubing string are indicated by failure of the string to maintain an adequate pressure level. If leaks are found, the tool is then moved up to different elevations in the string and additional tests are run. If the pressure is not held for a period of time, a leak above the tool is again indicated. The joint of tubing which leaks can thus be located by successive tests. The apparatus of the present invention can be used to take multiple readings so that pressure retention of the tubing string is observed. The rate of drop of pressure during a retention test and the depth of the tool in the string can be used to locate and estimate the size of a leak, thereby enabling repairs to the tubing string.